Justification:Libellula angelina was recorded at 86 localities in 29 prefectures until the 1950s. It declined in the 1960s, with drastic declines in the 1990s. In 2000 it was found at only 18 localities in six prefectures. Developments have destroyed and degraded habitat and introduced predators threaten the species directly. These declines are expected to continue.

Filling up of ponds to build houses and factories, and reforming to artificial ponds with concrete banks have much diminished the habitats. Destruction of grassy fields caused decrease of this species because the females and immature males need such fields as refuges. Introducing alien animals like Procambarus clarkii (Crustacea) and Micropterus salmoides (carnivorous fish) is a serious problem because of direct predation and habitat destruction.

The Ministry of Environment started to protect this species in 1993, and collection is prohibited by law. But this is not enough for the protection of habitats from destruction. Some NGOs have begun to conserve this insect and its habitats, for example at Okegaya Pond, Shizuoka Pref., Imuta Pond, Kagoshima Pref. and Noyori-shin Pond, Oita Pref.